Is this about CAPTCHA on web pages to make sure that a human person enters the data?
*http://en.wikipedia.org/wiki/Captcha
If there is an audio button, but the sound isn't working then there is a problem with the plugin that is used or the audio content is blocked.
*https://support.mozilla.org/kb/fix-common-audio-and-video-issues
*http://kb.mozillazine.org/Video_or_audio_does_not_play